Reducing odors with a germicidal lamp

ABSTRACT

A mechanical ventilation system, which obtains and maintains to below threshold reduced concentrations of volatile organic compounds and common organic odors in an air stream. The air stream has a concentration of volatile organic compounds of at least 100 parts per million and a temperature of between 30° and 70° F. The mechanical ventilation system comprises a duct, an air moving apparatus and a low-pressure germicidal lamp. The duct has a volume of at least five cubic feet for temporally containing and directing the air stream. The air moving apparatus moves the air stream through the duct at a speed of at least 100 cubic feet per minute. The low-pressure germicidal lamp is installed with respect to the duct such that the germicidal lamp, when energized, will irradiate the air stream passing through the duct. The germicidal lamp, when energized, produces ultraviolet radiation of approximately 254 nm with a power of at least 300 microwatts/cm 2  at 1 meter for every 4 square feet of duct area, with substantially no ozone generated. Application of the ultraviolet light to the air stream reduces concentrations of volatile organic compounds and other common organic odors in an air stream to below thresholds such as ordinary olfactory detection.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates generally to methods and apparatusfor achieving and maintaining acceptable indoor air quality.

[0003] 2. Description Of Related Art

[0004] One industry that is mature and economically sensitive to costsis the heating, ventilation and air conditioning (HVAC) industry.Because of the competitive nature of both the construction and HVACindustries, HVAC systems must be inexpensive to purchase and install. Ofa more global interest though, is the cost to operate and maintain HVACsystems. Often, a building owner will replace an aging HVAC system asthe reduction in operating and maintenance costs can offset the retrofitcost, sometimes in a matter of months.

[0005] HVAC systems are typically comprised of a cooling and heatingsection for, respectively, cooling and heating the air. An HVAC systemwill also include fans and ductwork for moving this conditioned airwhere it is needed. In most HVAC systems, air is drawn in, filtered,cooled and dehumidified or heated and humidified, and then delivered toa space. The greatest portion of this air is drawn from the space forrecirculation through the HVAC system.

[0006] One factor impacting design and operation of HVAC systems isindoor air quality (IAQ). A major consideration in IAQ today is theamount of outdoor air introduced by an HVAC system into an otherwisesealed space. The HVAC industry and others have adopted standards forthe introduction of outdoor air into spaces serviced by an otherwiseclosed HVAC system. These include offices, residential, commercial,industrial and institutional spaces, as modes of transportation such ascars, buses, planes and ships. In addition to controlling indoor air foroccupant comfort, the goal of most HVAC systems is to provide air withreduced levels of particulate, gases and bioaerosols, be it forsemiconductor, pharmaceutical or food processing facilities, hospitals,schools or offices and now the home.

[0007] Various reasons have contributed to the lack of success inutilizing germicidal lamps for bioaerosol control (IAQ), except forlimited and specialized purposes. The functional implementation of suchdevices in air moving systems has been limited generally to expensiveportable units with questionable efficacy. However, non-moving airdevices can be found as wall or ceiling mount systems where thegermicidal lamp is situated in a minimum air movement, and properambient air temperature area. A typical germicidal tube is designed tooperate in still air of 80-90° F. to maintain a tube wall temperature of105° F. Germicidal lamps have sensitive physical characteristicsincluding plasma gas(es), mercury and partial pressures thereof.

[0008] When a conventional germicidal lamp is used to irradiate movingairstreams, the air moving across the tube removes heat and lowers thetube's temperature. The tube's mercury begins to condense such that theemission of the germicidal wavelength of 253.7 nm decreases. Thisdecrease can be up to 75% when the tube wall temperature reaches 58° F.Also, at lower internal temperatures, tube components degrade quicker,shortening tube life. This phenomenon, known as skin effect cooling,requires a notable increase in the number of conventional tubes requiredfor a given level of performance. Increasing the number of tubes reducesthe available square area for airflow. This in turn requires the airs'velocity to increase, which decreases the dose (time times intensity)and air volume. If such a system could be made to work, it would requirean increase in fan horsepower, UVC light energy and in the number ofexpensive tube replacements.

[0009] Conventional germicidal lamps emit ultraviolet light at both theprimary and secondary emission lines of mercury (254 nm and 187 nm). Atmercury's 187-nm line, ozone is created and in many applications ofgermicidal lamps, such as in water, this is desirable. However, ozonehas strict threshold limit values in air due to its strong oxidativeproperties and harm to humans. Also, numerous companies have attemptedto apply germicidal lamps to HVAC systems, these conventional germicidallamps have proved unsatisfactory. Typically, a conventional germicidallamp performs best when installed in a device or room where the air isstill and/or warm. So despite the clear benefits of germicidal lamps,problems such as decreased output in moving and/or low temperature air,reduced air changes and ozone production have prevented their use in allbut specialized environments.

[0010] Germicidal fixtures continue to enter the HVAC market. Recententries have been sold under the Germ-O-Ray and Germitroll trademarks.The particular capabilities and design of these devices is not known tothe inventors, though it is believed both devices use conventional tubesso that when installed in air ducts, they will suffer from the criteriaoutlined above.

[0011] For further information concerning improvements in electricdischarge devices, which are directed to overcoming such problems,reference is made to the above-identified patent applications. Theseother patent applications describe excellent devices and methods forusing germicidal lamps to make HVAC systems more efficient, less costlyto operate and maintain, and to provide better IAQ for a healthierenvironment.

[0012] Germicidal tubes differ significantly from electric dischargedevices used in ultraviolet gas spectroscopy (VUV tubes). Germicidaltubes are low-pressure types that emit UV light at the primary andsecondary emission lines of mercury—254 nm and 187 nm. In contrast, VUVtubes are high-pressure types that operate at high temperatures and as aconsequence, emit different spectral lines and intensities.

[0013] In occupant air one group of gas phase contaminants areclassified as volatile organic compounds (VOCs). VOCs have beenassociated with simple unpleasant odors to serious maladies. Many peoplecan detect even low part per billion (ppb) concentrations of VOCs in theair, and VOCs can be found in concentrations of parts per million (ppm).Numerous studies show the human nose to be the best gas chromatographand further that many people have mild to serious sensitivities tocertain or mixed VOCs and their associated odors. In higherconcentrations, some VOCs can cause physical discomfort and maladiesrequiring medical attention. Since newer buildings have become moreenergy efficient (tighter), internally generated VOCs are of greaterconcern.

[0014] Some level of VOCs and other organic odors have existed in newand old buildings alike for decades. Mechanically ventilated spacesaccumulate simple organic gas phase compounds as a result of operatingoffice equipment, adding new building materials or furnishings and usingvarious cleaning agents and solvents to name a few.

[0015] When attempting to rectify IAQ problems, gaseous contaminants canbe diluted (controlled) through the introduction of outside air.However, diluting VOCs with outdoor air is neither efficient nor costeffective. It requires both more heating and cooling to condition thisair and it may bring in more pollutants than it dilutes.

[0016] Other prior art methods include filtering air through activatedcarbon or activated alumina encapsulated by potassium permanganate, toeither adsorb the VOCs or to chemically react with them in an effort tobreak them down (oxidize). Both of these methods have certaindisadvantages. Both filtering devices require additional space andstructure within the ventilation system as they can be 24″×24″×24″ forevery 2000 cfm and weigh over 110 pounds each. Additionally, theyrequire added system static pressure (in air horsepower) to move airthrough them. Both require lots of natural resources to eitherreactivate or dispose of as hazardous waste fill. The initial cost toinstall these filters, excluding labor, is approximately $850 for every2000 cfm. Their maintenance costs are from $290 to $400 annually. Aproperly designed activated carbon system lasts approximately 12 months.A properly designed potassium permanganate encapsulated activatedalumina system lasts approximately 9 months. Thus, at least once peryear, these special filters require expensive, hazardous and intrusiveservice. These systems also require more air horsepower to move airthrough them and thus more energy consumed. When they are added to anexisting system, it could necessitate speeding up the fan and/orchanging out the fan and fan motor to a larger size.

[0017] Outside of HVAC, VOC-control has been pursued through severaltechniques. One technique uses liquids to wash VOCs from a gas stream.However, these liquid systems are inadequate for treating air in an HVACsystem. They can be more costly and hazardous than the filter systemsdescribed above. Heat treatment using radiant beds or afterburners hasbeen used to partially catalyze VOCs in certain applications. However,heat treatment is not compatible with HVAC systems. The amount of heatthat is added would also have to be offset by added cooling capacity.Photocatalysis has been gaining popularity in high VOC concentrationatmospheres but again first and operating costs are prohibitive. Solventrecovery systems utilizing high volumes of activated carbon are theextreme and here we are simply dealing with a misapplication.

[0018] UVC at predominately 253.7 nm in and of itself has not beenconsidered for VOC control. One prior art method used ultraviolet lightof 185 nm to produce ozone for breaking down odor. In that prior artmethod, an air stream was passed across an ultraviolet lamp of UV energyat 185 nm where oxygen (O₂) is separated forming unstable O₁'s, whichcombine with O₂'s to form O₃'s or ozone. Also, it was found that when anultraviolet lamp was placed in a moving air stream, the reduced UVoutput was insufficient enough to reduce the production of both 185 nmgenerated ozone and 253.7 nm UVC to have much effect on most VOCs. Thus,reliance only upon ultraviolet light even when producing ozone wasconsidered wholly inadequate for VOC-control.

SUMMARY OF THE INVENTION

[0019] The previously described problems are solved in a method andapparatus for reducing ppb concentrations of volatile organic compoundsand common organic odors to below threshold limit values in amechanically ventilated space. The mechanically ventilated space has amechanical ventilation system comprising plural ducts and an air movingapparatus such as a fan. Ultraviolet radiation is introduced into a ductto treat an air stream passing by the UV radiation and moving throughthe duct. The air stream passes at a speed of at least 100 to over 1500feet per minute and has a temperature of between 30° and 90° F. Anuntreated air stream could have a concentration of volatile organiccompounds as high as 100 parts per million.

[0020] A low-pressure germicidal lamp is installed with respect to theinterior of the duct such that the germicidal lamp, when energized, willirradiate the air stream. The germicidal lamp when energized emitsultraviolet radiation of approximately 254 nm with a power of at least30 to 3000 microwatts/cm² at 1 meter for every 4 square feet of ductarea, with substantially no ozone generated. The UV ionization radiationseparates many volatile organic compounds at the molecular and atomiclevel to water vapor and carbon dioxide thereby lowering theconcentration of volatile organic compounds to 90 parts per million anddown to 10 parts per billion.

[0021] Still further objects and advantages attaching to the device andto its use and operation will be apparent to those skilled in the artfrom the following particular description.

DESCRIPTION OF THE DRAWINGS

[0022] Further objects of this invention, together with additionalfeatures contributing thereto and advantages accruing therefrom, will beapparent from the following description of a preferred embodiment of thepresent invention which is shown in the accompanying drawings with likereference numerals indicating corresponding parts throughout and whichis to be read in conjunction with the following drawings, wherein:

[0023]FIG. 1 is a cross section of a duct having dual, single-endedgermicidal tubes installed therein.

[0024]FIG. 2 is a cross section of a germicidal tube in a duct andshowing the radiation pattern of ultraviolet light from the tube.

[0025] These and additional embodiments of the invention may now bebetter understood by tuning to the following detailed descriptionwherein an illustrated embodiment is described.

DETAILED DESCRIPTION OF THE INVENTION

[0026] Throughout this description, the embodiments and examples shownshould be considered as exemplars, rather than limitations on theapparatus and methods of the present invention.

[0027] Throughout this description, the preferred embodiment andexamples shown should be considered as exemplars, rather thanlimitations on the apparatus and methods of the present invention.

[0028] The sun naturally produces ionizing radiation. This radiation candisturb the electrical properties of most organic compounds, and at highenough levels will break apart these organic compounds at the molecularand atomic level. The residual compounds of such broken organiccompounds are mostly water vapor and carbon dioxide—harmless materialsin almost any environment. Yet, for reasons suggested above, sunlightcannot be used efficiently and effectively in a mechanically ventilatedspace for control of VOCs. A mechanically ventilated space is defined asspace which can be occupied by a person and having a mechanicalventilation system comprising plural ducts and which modifies airtemperature and possibly humidity for human comfort.

[0029] The inventors have found a way to replicate sunlight'sdegradation of VOCs without the problems of sunlight and at a low cost.That method comprises generating specific wavelengths of ultravioletradiation and directing that radiation into a moving air stream, whichflows into the mechanically ventilated and occupied space.

[0030] Turning now to FIG. 1, there is shown a cross-section of a duct100 of a mechanical ventilation system. FIG. 1 also shows a germicidallamp 200 comprising two tubes 210 and a fixture 220. Air passing throughthe duct typically will have a temperature of between 30°-70° F. Thehumidity of this air is also typically controlled. The relatively lowtemperature and varying humidity render the duct a harsh environment forelectronic devices, and particularly for germicidal lamps. For thegermicidal lamp to operate effectively in the harsh environs of an airduct, a germicidal lamp specifically designed for such an environmentsmust be employed. In particular, the germicidal lamps sold by theassignee of this invention, Steril-Air U.S.A., Inc, and sold under thetrademark, “UVC Emitter,” are preferred. These germicidal lamps produceno detectable ozone, which is also highly desirable. However, germicidallamps which produce an insignificant quantity of ozone may be used.

[0031] The mechanical ventilation system includes an air movingapparatus. This air moving apparatus is preferably a fan 120. The fan120 is shown in the duct 100, though the fan or other air movingapparatus may be located some distance from the germicidal lamp 200.Other air moving apparatuses which can move an air stream through theduct as described further below are within the scope of the invention.

[0032] In determining the spatial relationship between the germicidaltubes 210 and the walls of the duct 100, the objective is to obtain auniform distribution of UV radiation across the duct 100. It has beendetermined that, for a germicidal tube which is positioned in accordancewith the invention, the spatial distribution of UV radiation followsprecisely that of a diffuse area source and, surprisingly, not anisotropic point source. The pattern of UV radiation from the preferredgermicidal lamp is shown in FIG. 2. It can be seen that although thegermicidal tube 210 is a source of radiation, the walls of the duct 100are effectively a secondary (reflected) source of UV radiation. Thediffuse radiation of the germicidal tubes 210 and diffuse reflection istherefore defined as a near field effect, not as an inverse square law.This finding is contrary to normal expectations, and therefore placementof germicidal tubes in accordance with the present invention results inthe need for fewer germicidal tubes. Put another way, when thegermicidal tubes 210 are positioned in sufficient proximity to the wallsof the duct 100, the intensity of UV radiation from the germicidal tubes210 at a given point is, to a degree, independent of the distance of thegermicidal tubes 210 from the given point.

[0033] As shown in FIG. 2 the photons emitted from a particular point onthe germicidal tube 210 radiate in all directions. Because FIG. 2 is anelevational view, the global radiation of these photons is not shown.These photons would, however, also radiate outwardly and inwardly fromthe plane of the paper upon which the planar representation isillustrated and from all surfaces of the tube 210.

[0034] In accordance with the invention, ultraviolet radiation from agermicidal lamp is used to reduce concentrations of VOCs and commonorganic odors to below threshold limit values in a mechanicallyventilated space. That threshold is preferably an average person'sability to smell the VOCs and common organic odors (“olfactorydetection”). To reduce VOCs and common organic odors below olfactorydetection, it is believed that the concentration of VOCs must be reducedto below 100 parts per billion. The ultraviolet radiation is appliedwithin the ductwork of the mechanical ventilation system of themechanically ventilated space. Ultraviolet light of 254 nm willinvalidate the molecular structure of a VOC in a confined air stream. Agermicidal lamp is preferably used to emit ultraviolet radiation ofapproximately 254 nm, with substantially no ozone generated. The absenceof ozone is a notable difference from most prior art methods as it isnow well understood that ozone is harmful to human health and more so inthe presence of certain VOCs.

[0035] In order to treat an appreciable quantity of air, the methodincludes directing the radiation into a relatively rapidly moving airstream. As a normal function of the operation of a mechanicalventilation system, air is passed through the system's ductwork.Preferably, the air stream has a speed of at least 100 feet per minute(FPM). More typically, the air stream has a speed of between 100 to over1500 feet per minute. The air in the duct preferably has a temperatureof between 30° and 90° F, which though not necessarily ideal for UVCtype ionization of the VOCs and common organic odors, renders the methodunobtrusive to operation of the mechanical ventilation system. Thequality of radiation introduced into the duct is adjusted to achieve thedesired results, rather than adjusting the temperature, air pressure orhumidity of the air stream to be treated. This is more easily achievedwith the product that the inventor offers.

[0036] The air is passed through a region of a duct having a volume ofat least four cubic feet for the irradiation cited. The inventors havefound that the air would have a concentration of volatile organiccompounds of 100 parts per million (PPM) or less for the method to beuseful.

[0037] To generate the ultraviolet radiation, a low pressure germicidallamp, such as that shown in FIG. 1, is preferably utilized. Thegermicidal lamp is preferably positioned with respect to the region suchthat the germicidal lamp, when energized, will irradiate the region andthe air stream which passes there through. The region preferably isirradiated with a power of at least 300 microwatts/cm² at 1 meter forevery 4 square feet of duct area

[0038] The germicidal lamp preferably comprises a single-ended tube anda fixture as described above. Installation of such a germicidal lampincludes producing a hole in the duct wall, mounting the fixture overthe hole on the outside of the duct, inserting the tube through a holein the fixture and in the duct wall, and securing the tube with thefixture. The fixture preferably includes a power supply adapted toreceive standard power available within the mechanical ventilationsystem. This typically is 115, 208/230 or 277 Vac power. Powerconsumption for a typical install of germicidal lamps is preferably lessthan 150 Watts per each 2000 CFM of duct air.

[0039] The tubes of the germicidal lamp are preferably distanced fromone another such that the duct area is equally irradiated with the tubecenterlines potentially based on a given concentration per unit volumeof offending VOC. Because of the low power consumption of the germicidallamps, the germicidal lamps can and should be operated at any time themechanical ventilation system is running.

[0040] The inventors have found that, when so applied, the UV radiationdestroys VOCs and common organic odors in the air stream to therebylower the VOC concentration to as little as 10 ppb. At such a low level,the VOCs and common organic odors are beyond human olfactory detectionand therefore is not a hazard or nuisance to building occupants.

[0041] In contrast to the cost and problems of the prior art methods ofVOC control described above, UVC irradiation can be less costly, morepredictable and as a monumental benefit, adds nothing to the environmentor the space being served.

[0042] Installation of properly sized single-ended germicidal lampsrequires little mechanical or physical modifications to an existingmechanical ventilation system. Thus, the method can be used in bothexisting and new mechanical ventilation systems, and the germicidallamps simply added to the existing structure. The inventors have foundthat germicidal lamps which emit UV of approximately 254 nm withoutsubstantial ozone require relatively little energy to operate, requireno changes to mechanical equipment and offer the additional benefit ofkilling (inactivating) microorganisms in the air.

[0043] Using UV light could reduce the amount of outdoor air fordilution or eliminate the need for adding sorbants to the air handler.The annual savings, including labor and materials for both could amountto $0.45 per CFM or more. Building owners and operators can reduce theirdependency on, or eliminate the need for, increased amounts of outdoorair thus eliminating the need or requirement to condition that air foracceptable use. Additionally, productivity would be increased whileabsenteeism or incapacitation would be decreased. Savings in both areaswould be dramatic.

[0044] Our method is especially non evasive to the typical air handlingsystem and can be directly related to the regenerative and restorativeproperties of our sun . It does not require altering the mechanicalequipment to install or operate. It has lower costs of installation,operation and maintenance. It adds nothing to the air stream orenvironment to control gas phase compounds. It also provides asignificant degree of germicidal control to further reduce absenteeismand incapacitation. Thus, the invention provides a more suitable indoorenvironment for occupants of any mechanically ventilated space whetherat work, school or leisure.

[0045] The streams in which the above described hydrocarbons are presentas contaminants are described as conditioned spaces designed for humanoccupancy. Such streams typically consist of air or of rather inertgases, such as nitrogen. These gaseous hydrocarbon contaminants may bepresent individually or admixed in concentrations as low as 10 parts perbillion (volume basis), and up to 100 parts per million. However, thepresent decontaminating process is sufficiently reactive to be ofconsiderable interest even well below 100-ppb hydrocarbon concentration.

[0046] As with many chemical reactions, increased temperature generallyaccelerates the decontaminating process; however, the photochemicalnature of the present process is rather insensitive to temperaturessignificantly below the thermal oxidation temperatures of the subjecthydrocarbons. Consequently, temperature limitations follow frompractical considerations. Similarly, the decontamination rate willincrease with increased ultraviolet radiation intensity. However, it isimportant to control the UV so that a base intensity exists for a givenconcentration of VOCs. The inventors have found that an untreated tubewall will allow out the 185-nm wavelength and will generate ozone.

[0047] The pressure at which the decontamination reaction is conductedis again limited by practical considerations. The air streams of thisprocess are subject to ordinary gas laws, and the effective residencetime obtained through selection of the air speed in the duct. Thedecontamination reaction per se is rather insensitive to pressure withinordinary limits of 0.01 to 10 Atmospheres.

[0048] Some oxygen must be present, as ultraviolet light is believedalso to react with both oxygen and background ozone to produce variousactivated species, including OH radicals, O₂H₂, O₁, O₂ and O₃ withexcited electron states. The term “oxygen species” refers collectivelyto these compounds and elements and their excited allotropes. The ductis selected to provide sufficient time to oxidize or break apart theVOCs into simple products such as carbon dioxide, water vapor andhydrogen halides.

[0049] Although exemplary embodiments of the present invention have beenshown and described, it will be apparent to those having ordinary skillin the art that a number of changes, modifications, or alterations tothe invention as described herein may be made, none of which depart fromthe spirit of the present invention. All such changes, modifications andalterations should therefore be seen as within the scope of the presentinvention.

It is claimed:
 1. A method of reducing concentrations of volatileorganic compounds and common organic odors to below threshold limitvalues of human detection in a mechanically ventilated space, themechanically ventilated space having a mechanical ventilation systemcomprising plural ducts, the method comprising the steps of: (a)identifying a region having a volume of at least four cubic feet withina given duct of the mechanical ventilation system through which an airstream passes at a speed of at least 100 cubic feet per minute, the airstream having a concentration of volatile organic compounds of at least100 parts per million and a temperature of between 30° and 70° F.; (b)installing a low pressure germicidal lamp with respect to the regionsuch that the germicidal lamp, when energized, will irradiate the regionand the air stream which passes there through; (c) energizing thegermicidal lamp and exposing the air stream to ultraviolet radiation ofapproximately 254 nm with a power of at least 300 microwatts/cm² at 1meter for every 4 square feet of duct area, with substantially no ozonegenerated; wherein the UV radiation destroys volatile organic compoundsin the air stream to thereby lower the concentration of volatile organiccompounds to potentially no more than 10 parts per million.
 2. Themethod of reducing concentrations of volatile organic compounds andcommon organic odors to below thresholds in a mechanically ventilatedspace of claim 1 wherein the air stream passes through the region of theduct at between 200 and 600 cubic feet per minute.
 3. The method ofreducing concentrations of volatile organic compounds and common organicodors to below thresholds in a mechanically ventilated space of claim 1wherein the germicidal lamp comprises a single-ended tube and a fixture,the installing step comprising: (a) opening a hole in the duct wall; (b)mounting the fixture over the hole on the outside of the duct; (c)inserting the tube through a hole in the fixture and the hole in theduct wall; and (d) securing the tube to the fixture.
 4. The method ofreducing concentrations of volatile organic compounds and common organicodors to below threshold in a mechanically ventilated space of claim 1,wherein the thresholds are comprised of human olfactory detection. 5.The method of reducing concentrations of volatile organic compounds andcommon organic odors to below thresholds in a mechanically ventilatedspace of claim 1, wherein the thresholds are less than 100 parts permillion.
 6. A method capable of controlling low levels of volatileorganic compounds (VOCs) and common organic odors in an air flow andcapable of operation at ambient and cool temperatures comprising: (a)passing the contaminated air flow through a duct, the air flow having aspeed of at least 100 cubic feet per minute, the air flow having aconcentration of volatile organic compounds of at least 100 parts permillion and a temperature of between 30° and 70° F.; (b) generatingultraviolet light of approximately 254 nm without generating asubstantial quantity of ozone; (c) directing the generated ultravioletlight into the duct with a power of at least 300 microwatts/cm² at 1meter for every 4 square feet of duct area, with substantially no ozonegenerated; (d) converting with the ultraviolet light the VOCs into nontoxic materials; wherein organic gas phase compounds are degraded tobelow threshold limit values.
 7. The method of controlling low levels ofVOCs and common organic odors in an air flow of claim 6 wherein theultraviolet light is generated by a germicidal lamp, the lamp comprisinga tube and a fixture, the duct having an inside and an outside, themethod further comprising the steps of: installing the fixture on theoutside of the duct; installing the tube into the fixture, wherein thetube extends into the duct.
 8. The method of controlling low levels ofVOCs and common organic odors in an air flow of claim 6 wherein the aircomprises at least 5% oxygen.
 9. The method of controlling low levels ofVOCs and common organic odors in an air flow of claim 6 wherein the aircomprises at least 25% nitrogen.
 10. The method of controlling lowlevels of VOCs and common organic odors in an airflow of claim 6 whereinthe amount of ultraviolet light directed into the duct is varied inrelation to the anticipated concentration of VOCs in the air stream. 11.The method of controlling low levels of VOCs and common organic odors inan air flow of claim 10 wherein the ultraviolet light is generated by agermicidal lamp, and the amount of ultraviolet light directed into theduct is varied by varying the intensity of ultraviolet light source. 12.The method of controlling low levels of VOCs and common organic odors inan air flow of claim 11 wherein the contaminant is a member selectedfrom the group consisting of: (a) aliphatic and aromatic hydrocarbons ina family commonly found indoors, (b) saturated and unsaturatedhydrocarbons containing 28 carbon atoms, (c) halogen substitutedsaturated and unsaturated hydrocarbons containing 28 carbon atoms, and(d) partially oxidized variants of the hydrocarbons and the halogensubstituted hydrocarbons.
 13. A mechanical ventilation system whichobtains and maintains to below threshold values reduced concentrationsof volatile organic compounds and common organic odors in an air stream,the air stream having a concentration of volatile organic compounds ofat least 100 parts per million and a temperature of between 30° and 70°F., the mechanical ventilation system comprising: (a) a duct having avolume of at least four cubic feet for temporally containing anddirecting the air stream, the duct comprising at least one wall which isair-tight and defining an interior through which the air stream passesand an exterior; (b) an air moving apparatus for moving the air streamthrough the duct at a speed of at least 100 cubic feet per minute; (c) alow pressure germicidal lamp installed with respect to the duct suchthat the germicidal lamp, when energized, will irradiate the air streampassing through the duct; (d) wherein the germicidal lamp, whenenergized, produces ultraviolet radiation of approximately 254 nm with apower of at least 300 microwatts/cm² at 1 meter for every 4 square feetof duct area, with substantially no ozone generated.
 14. The mechanicalventilation system of claim 13 wherein the air moving apparatus movesthe air stream through the duct at between 200 and 600 cubic feet perminute.
 15. The mechanical ventilation system of claim 13 wherein thegermicidal lamp comprises: a fixture disposed exterior to the duct; anda single-ended tube substantially disposed within the duct andelectrically connected to the fixture and supported by the fixture. 16.The mechanical ventilation system of claim 13 wherein the thresholdlimit values are comprised of concentrations specific to the compoundthat produces human olfactory detection.
 17. The mechanical ventilationsystem of claim 13 wherein the threshold comprises 100 parts perbillion.